FLiNaK熔盐中CsF的蒸发与分离

Cs的同位素是核裂变的主要产物之一,在熔盐反应堆液态燃料盐中以Cs F的化学形态存在,定期从燃料盐中除去或减少其含量将有助于提高反应堆的中子经济性。本文用FLi Na K熔盐模拟熔盐堆载体盐FLi Be体系,研究了Cs F在不同蒸发条件下的蒸发行为,并尝试进行了减压蒸馏和金属Li还原蒸发技术分离Cs F的实验研究。研究表明,在5 Pa蒸馏压力下,Cs F的蒸发量随温度呈线性上升趋势,780oC时Cs F的含量由1%降到0.14%,分离率达86%,但此时载体盐的蒸发量达9.5%;在常压、700oC条件下,熔盐中Cs F的蒸发比例随还原剂Li的添加量而提高,当添加的金属Li的摩尔浓度与Cs F为120:1时,Cs F分离率达91%。研究结果为了解Cs F在氟盐体系中的蒸发行为和建立可行的分离方法提供基础实验依据。

Evaporation and separation of CsF in FLiNaK molten salt

Background: The removal of CsF, a major fission product in molten salt reactor, on a regular basis is helpful for the improvement of neutron economy of the reactor.Purpose: This study aims to investigate the evaporation behavior of CsF under different experimental conditions in FLiNaK molten salt.Methods: Two different evaporation methods, namely vacuum distillation and reductive evaporation by metal lithium, were employed in this work.Results: The results from the experiments of vacuum distillation at 5 Pa revealed a linear correlation between evaporated mass of CsF and evaporation temperature. At 780 oC, the CsF concentration in molten salt decreased from 1% to 0.14% upon distillation with a separation rate of 86% despite the loss of 9.5% of the carrier salt. Reductive evaporation by metal lithium was carried out at 700℃ and 1.01×105Pa. The amount of evaporated CsF increased with the increase of lithium added into the molten salt. The separation rate was 91% at a molar ratio of lithium to CsF of 120.Conclusion: Fundamental data are provided to understand the evaporation behaviors of CsF in fluoride molten salt, which could further benefit the establishment of efficient separation technique for CsF removal from spent fuel.